This invention relates to a resin-stripping die used in filament-winding processes in which resin-impregnated strands of continuous glass fiber rovings are wrapped around a mandrel and subsequently cured. The present state of the art in filament winding and impregnating of strands of glass fibers is dislosed in an Owens-Corning Fiberglas Bulletin entitled Filament Winding With Type 30 Roving (Pub. #5-CR-6516). This bulletin discloses in FIG. 9 one of the most common commercial processes for impregnation of the glass fibers wherein the strands are fed across a moving roll and pick up a given amount of resin. That Bulletin specifically discusses a resin-stripping orifice to remove excess resin, such resin stripping apparatus have been used in the prior art.
In filament winding, pultrusion and other processes, it is desirable to saturate the fibrous strands of glass or other fibers with resin or other plastisol before forming them into the shape of the final article. The excess resin then needs to be removed. In most filament winding operations, the excess is often squeezed off by rubber squeegees which add tension and may cause strand breakage. Such conventional apparatus leaves undesirable excess resin to be wasted or collected mechanically or manually when it drips off the mandrel.
Prior art stripping dies used to remove excess resin are usually of a type difficult to thread. Experiments have shown that round cross-section dies give the lowest back tension and less strand breakage. One such prior art die is disclosed by U.S. Pat. No. 2,960,063 to Martuch. This die consists of half-cone members which form an opening or passage through which a glass strand is passed in order to remove excess resin. These half-cone members are adjustable relatively to vary the size of the strand passage so as to vary the size of the strand along its length. As the strand moves through the passage, it tends to spread laterally thorugh the split between the die halves and the resin will also escape through the split. Thus, there will be a distortion of the cross-sectional shape of the strand and the resin will not be applied uniformaly thereto to provide a strand of circular cross-section with a uniform coating of predetermined thickness. Also, this die could not be readily slipped over a strand due to the complicated and cumbersome adjustable mounting for the two halves.
The main problem for conventional stripping dies is to prevent excess resin on strands leaving the impregnation bath. With conventional stripping dies the impregnated bundle of fibers or strands comprises about 50% by weight of resin which is about 70% of the volume.
For purposes of this disclosure the fibers or strands to be impregnated or coated include glass fiber, aramid, graphite or any other fibers needing such treatment.
For purposes of this disclosure the impregnating or coating resin may be epoxy, vinyl ester, polyester and the like.